Method of making endovascular support device

ABSTRACT

An endovascular support device for treatment of chronic restenosis or other vascular narrowing is disclosed together with a method of manufacture and a method for delivering a plurality of such devices to an affected area of a vessel. In a preferred embodiment, the endovascular support device comprises a unitary wire-like structure configured to form a plurality of upper and lower peaks which may be compressed for delivery to an affected area of a coronary or peripheral vessel in a human, and then expanded to maintain a passageway through the vessel.

This application is a division of application Ser. No. 08/172,420, filedDec. 22, 1993, now abandoned, which is a division of application Ser.No. 07/398,180, filed Aug. 24, 1989, now U.S. Pat. No. 5,292,331.

SPECIFICATION

1. Field of the Invention

The present invention relates generally to medical devices, andparticularly relates to implantable devices for treating narrowing ofcoronary or peripheral vessels in humans.

2. Background of the Invention

Cardiovascular disease, including atherosclerosis, is the leading causeof death in the U.S. The medical community has developed a number ofmethods for treating coronary heart disease, some of which arespecifically designed to treat the complications resulting fromatherosclerosis and other forms of coronary arterial narrowing.

The most impelling development in the past decade for treatingatherosclerosis and other forms of coronary narrowing is percutaneoustransluminal coronary angioplasty, hereinafter referred to simply as"angioplasty" or "PTCA". The objective in angioplasty is to enlarge thelumen of the affected coronary artery by radial hydraulic expansion. Theprocedure is accomplished by inflating a balloon within the narrowedlumen of the coronary artery. Radial expansion of the coronary arteryoccurs in several different dimensions and is related to the nature ofthe plaque. Soft, fatty plaque deposits are flattened by the balloon andhardened deposits are cracked and split to enlarge the lumen. The wallof the artery itself is also stretched when the balloon is inflated.

PTCA is performed as follows: A thin-walled, hollow guiding catheter istypically introduced into the body via a relatively large vessel, suchas the femoral artery in the groin area or the brachial artery in thearm. Access to the femoral artery is achieved by introducing a largebore needle directly into the femoral artery, a procedure known as theSeldinger Technique. Once access to the femoral artery is achieved, ashort hollow sheath is inserted to maintain a passageway during PTCA.The flexible guiding catheter, which is typically polymer coated, andlined with Teflon, is inserted through the sheath into the femoralartery. The guiding catheter is advanced through the femoral artery intothe iliac artery and into the ascending aorta. Further advancement ofthe flexible catheter involves the negotiation of an approximately 180degree turn through the aortic arch to allow the guiding catheter todescend into the aortic cusp where entry may be gained to either theleft or the right coronary artery, as desired.

After the guiding catheter is advanced to the ostium of the coronaryartery to be treated by PTCA, a flexible guidewire is inserted into theguiding catheter through a balloon and advanced to the area to betreated. The guidewire provides the necessary steerability for lesionpassage. The guidewire is advanced across the lesion, or "wires" thelesion, in preparation for the advancement of a polyethylene, polyvinylchloride, polyolefin, or other suitable substance balloon catheteracross the guide wire. The balloon, or dilatation, catheter is placedinto position by sliding it along the guide wire. The use of therelatively rigid guide wire is necessary to advance the catheter throughthe narrowed lumen of the artery and to direct the balloon, which istypically quite flexible, across the lesion. Radiopaque markers in theballoon segment of the catheter facilitate positioning across thelesion. The balloon catheter is then inflated with contrast material topermit fluoroscopic viewing during treatment. The balloon is alternatelyinflated and deflated until the lumen of the artery is satisfactorilyenlarged.

Unfortunately, while the affected artery can be enlarged, in someinstances the vessel restenoses chronically, or closes down acutely,negating the positive effect of the angioplasty procedure. In the past,such restenosis has frequently necessitated repeat PTCA or open heartsurgery. While such restenosis does not occur in the majority of cases,it occurs frequently enough that such complications comprise asignificant percentage of the overall failures of the PTCA procedure,for example, twenty-five to thirty-five percent of such failures.

To lessen the risk of restenosis, various devices have been proposed formechanically keeping the affected vessel open after completion of theangioplasty procedure. Such mechanical endoprosthetic devices, which aregenerally referred to as stents, are typically inserted into the vessel,positioned across the lesion, and then expanded to keep the passagewayclear. Effectively, the stent overcomes the natural tendency of thevessel walls of some patients to close back down, thereby maintaining amore normal flow of blood through that vessel than would be possible ifthe stent were not in place.

Various types of stents have been proposed, although to date none hasproven satisfactory. One proposed stent involves a tube of stainlesswire braid. During insertion, the tube is positioned along a deliverydevice, such as a catheter, in extended form, making the tube diameteras small as possible. When the stent is positioned across the lesion, itis expanded, causing the length of the tube to contract and the diameterto expand. Depending on the materials used in construction of the stent,the tube maintains the new shape either through mechanical force orotherwise. For example, one such stent is a self-expanding stainlesssteel wire braid. Other forms of stents include various types tubularmetallic cylinders expanded by balloon dilatation. One such device isreferred to as the Palmaz stent, discussed further below.

Another form of stent is a heat expandable device. This device,originally designed using NITINOL by Dotter has recently been modifiedto a new tin-coated, heat expandable coil by Regan. The stent isdelivered to the affected area on a catheter capable of receiving heatedfluids. Once properly positioned, heated saline is passed through theportion of the catheter on which the stent is located, causing the stentto expand. Numerous difficulties have been encountered with this device,including difficulty in obtaining reliable expansion, and difficultiesin maintaining the stent in its expanded state.

Perhaps the most popular stent presently under investigation in theUnited States is referred to as the Palmaz stent. The Palmaz stentinvolves what may be thought of as a stainless steel cylinder having anumber of slits in its circumference, resulting in a mesh when expanded.The stainless steel cylinder is delivered to the affected area by meansof a balloon catheter, and is then expanded to the proper size byinflating the balloon.

Significant difficulties have been encountered with all prior artstents. Each has its percentage of thrombosis, restenosis and tissuein-growth, as well as varying degrees of difficulty in deployment.Another difficulty with at least some of prior art stents is that theydo not readily conform to the vessel shape. In addition, the relativelylong length of such prior art stents has made it difficult to treatcurved vessels, and has also effectively prevented successfulimplantation of multiple such stents. Anticoagulants have historicallybeen required at least for the first three months after placement. Theseand other complications have resulted in a low level of acceptance forsuch stents within the medical community, and to date stents have notbeen accepted as a practical method for treating chronic restenosis.

Thus there has been a long felt need for a stent which is effective tomaintain a vessel open, without resulting in significant thrombosis,which may be easily delivered to the affected area, easily expanded tothe desired size, easily conformed to the affected vessel, and easilyused in multiples to treat curved vessels and varying lengths oflesions.

SUMMARY OF THE INVENTION

The present invention substantially reduces the complications andovercomes the limitations of the prior art devices. The endovascularsupport device of the present invention comprises a device having verylow mass which is capable of being delivered to the affected area bymeans of a slightly modified conventional balloon catheter similar tothat used in a standard balloon angioplasty procedure.

The support device of the present invention may then be expanded bynormal expansion of the balloon catheter used to deliver the stent tothe affected area, and its size can be adjusted within a relativelybroad range in accordance with the diagnosis of the treating physician.

Because of the range of diameters through which the support device ofthe present invention may be expanded, it may be custom expanded to thespecific lesion diameter, and is readily conformable to the vesselshape. In addition, a plurality of support devices of the presentinvention may be readily implanted in a number commensurate with thelength of the lesion under treatment. As a result, curved or "S" shapedvessels may be treated.

The stent, or endovascular support device, of the present invention maypreferably be comprised of implantable quality high grade stainlesssteel, machined specially for intravascular applications. The supportdevice may comprise, in effect, a metal circle or ellipsoid formed tocreate a plurality of axial bends, thereby permitting compression of thestent onto a delivery catheter, and subsequent expansion once in placeat the affected area.

It is one object of the present invention to provide a stent whichsubstantially overcomes the limitations of the prior art.

It is a further object of the present invention to provide a stentcapable of being implanted simply and reliably.

Another object of the present invention is to provide a stent which doesnot result in significant thrombosis at the point of implant.

Yet another object of the present invention is to provide a stent whichcan be selectively sized in accordance with the anatomic configurationdictated by the lesion itself.

A still further object of the present invention is to provide a methodfor supplying an endovascular support device which permits a pluralityof such devices to be implanted commensurate with the length of thelesion under treatment.

These and other objects of the present invention can be betterappreciated from the following detailed description of the invention,taken in conjunction with the attached drawings.

FIGURES

FIG. 1 shows a perspective view of an endovascular support deviceconstructed according to the present invention, in its expanded form.

FIG. 2 shows a support device constructed according to the presentinvention and compressed onto a balloon catheter.

FIG. 3 shows a support device compressed onto a balloon catheter asshown in FIG. 2, and positioned within a sectioned portion of anaffected area of a artery or other vessel.

FIG. 4 shows a support device according to the present invention in itsexpanded form within a sectioned portion of a vessel including a lesion.

FIG. 5 shows a support device of the present invention in its expandedform within a sectioned portion of a lesion after removal of the ballooncatheter.

FIGS. 6a-b show alternative configurations of a support device accordingto the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring first to FIG. 1, an endovascular support device 10, referredto hereinafter more conveniently as a stent, constructed in accordancewith the present invention can be seen in perspective view. The stent 10of FIG. 1 is shown in its expanded form, prior to compression over asuitable delivery system as discussed in detail hereinafter.

In a preferred embodiment, the stent 10 comprises a single piece ofmaterial, bent to form a plurality of upper axial turns 12 and loweraxial turns 14. In the embodiment shown in FIG. 1, four upper turns 12are connected to the four lower turns 14 by substantially straightsegments 16. The axial turns 12 and 14 can be seen to permit the stent10 to be compressed or expanded over a wide range while stillmaintaining significant mechanical force, such as required to prevent avessel from restenosing. While a preferred embodiment comprises a singlepiece of material, in some instances a suitably welded wire may beacceptable.

It will be appreciated that the number of turns 12 and 14 can vary overa reasonably wide range, defined in "N" number of turns, and may in factvary between two and ten such turns or peaks. However, it is currentlybelieved that the optimum number of turns or peaks will range betweenthree and five for most applications, and particularly forcardiovascular applications.

The stent 10 is preferably constructed of implantable materials havinggood mechanical strength. An embodiment which has proven successful inpreliminary testing is machined from 316LSS implantable qualitystainless steel bar stock. The bar stock is machined to formsubstantially a toroid, which is then acid etched in phosphoric andsulfuric acid at approximately 180. to 185. to break the edges. Theetched toroid is then plated with copper to avoid galling and to providelubricity.

The copper plated toroid is then bent to the shape of the stent 10 shownin FIG. 1, after which the copper plating is stripped from the stent.The stent is then returned to the acid bath to reduce the wire size tothe desired diameter, which is in the range of 0.002" to 0.025". It ispresently believed that the optimum wire size for the final product isin the range of 0.008" to 0.009". It will be appreciated that thestrength of the stent--that is, its ability to prevent restenosis--isinversely proportional to the number of peaks or turns in the stent, sothat stents having a greater number of turns will typically be formed oflarger wire diameters. Finally, although not required in all cases, theoutside of the stent may be selectively plated with platinum to provideimproved visibility during fluoroscopy. The cross-sectional shape of thefinished stent may be circular, ellipsoidal, rectangular, hexagonal,square, or other polygon, although at present it is believed thatcircular or ellipsoidal may be preferable.

The minimum length of the stent, or the distance between the upper turns12 and lower turns 14, is determined in large measure by the size of thevessel into which the stent will be implanted. The stent 10 willpreferably be of sufficient length as to maintain its axial orientationwithin the vessel without shifting under the hydraulics of blood flow(or other fluid flow in different types of vessels), while also beinglong enough to extend across at least a significant portion of theaffected area. At the same time, the stent should be short enough as tonot introduce unnecessarily large amounts of material as might causeundue thrombosis. Typical cardiovascular vessels into which the stent 10might be implanted range from 1.5 millimeters to five millimeters indiameter, and corresponding stents may range from one millimeter to twocentimeters in length. However, in most instances the stent will rangein length between 3.5 millimeters and 6 millimeters. Preliminary testingof stents having a length between 3.5 millimeters and 4.5 millimetershas been performed with good success outside the United States, andtesting on animals is also ongoing.

Once the wire size of the stent 10 has been reduced to the desired size,the stent 10 may be crimped onto a balloon 100, as shown in FIG. 2, fordelivery to the affected region 102 of a vessel 104 such as a coronaryartery. For the sake of simplicity, the multiple layers of the vesselwall 104 are shown as a single layer, although it will be understood bythose skilled in the art that the lesion typically is a plaque depositwithin the intima of the vessel 104.

One suitable balloon for delivery of the stent 10 is manufactured byAdvanced Cardiovascular Systems, Inc., of Santa Clara, Calif. ("ACS"),and is eight millimeters in length with Microglide® on the shaft only.The stent-carrying balloon 100 is then advanced to the affected area andacross the lesion 102 in a conventional manner, such as by use of aguide wire and a guide catheter (not shown). A suitable guide wire isthe 0.014" Hi Torque Floppy manufactured by ACS, and a suitable guidingcatheter is the ET.076 lumen guide catheter, also manufactured by ACS.

Once the balloon 100 is in place across the lesion 102, as shown in FIG.3, the balloon 100 may be inflated, again substantially in aconventional manner. In selecting a balloon, it is helpful to ensurethat the balloon will provide radially uniform inflation so that thestent 10 will expand equally along each of the peaks. The inflation ofthe balloon 100, shown in FIG. 4, causes the expansion of the stent 10from its crimped configuration back to a shape substantially like thatshown in FIG. 1. The amount of inflation, and commensurate amount ofexpansion of the stent 10, may be varied as dictated by the lesionitself, making the stent of the present invention particularly flexiblein the treatment of chronic restenosis.

Because of the inflation of the balloon, the lesion 102 in the vessel104 is expanded, and causes the arterial wall of the vessel 104 to bulgeradially, as simplistically depicted in FIG. 4. At the same time, theplaque deposited within the intima of the vessel is displaced andthinned, and the stent 10 is embedded in the plaque or other fibroticmaterial adhering to the intima of the vessel 104.

Following inflation of the balloon 100 and expansion of the stent 10within the vessel 104, the balloon is deflated and removed. The exteriorwall of the vessel 104 returns to its original shape through elasticrecoil. The stent 10, however, remains in its expanded form within thevessel, and prevents further restenosis of the vessel. The stentmaintains an open passageway through the vessel, as shown in FIG. 4, solong as the tendency toward restenosis is not greater than themechanical strength of the stent 10. Because of the low mass of thesupport device 10 of the present invention, thrombosis is less likely tooccur. Ideally, the displacement of the plaque deposits and theimplantation of the stent 10 will result in a smooth inside diameter ofthe vessel 104, although this ideal cannot be achieved in all cases.

One of the advantages of the stent 10 is that multiple stents, "M", maybe used in the treatment of a single lesion. Thus, for example, in theevent the affected area shown in FIGS. 3 and 4 was longer than the stent10, additional stents 10 could be positioned elsewhere along the lesionto prevent restenosis. In preliminary testing, up to four stents havebeen used successfully along a single lesion. Due to the conformabilityof the stent 10, not only can varying lesion lengths be treated, butcurved vessels and "S" shaped vessels may also be treated by the presentinvention. In instances where it is known in advance that multiplestents will be the preferred method of treatment, a plurality of suchstents, "M" may be positioned along a single balloon catheter forsimultaneous delivery to the affected area.

As discussed above, the number of peaks or turns 12 and 14 in the stent10, "N" number of turns, may vary between two and ten. To this end,shown in FIGS. 6a and 6b are two alternative configurations of the stent10. The alternative embodiment shown in 6a can be seen to have threeupper and three lower peaks or turns, while the embodiment shown in FIG.6b can be seen to have ten upper and ten lower peaks.

While the primary application for the stent 10 is presently believed tobe treatment of cardiovascular disease such as atherosclerosis or otherforms of coronary narrowing, the stent 10 of the present invention mayalso be used for treatment of narrowed vessels in the kidney, leg,carotid, or elsewhere in the body. In such other vessels, the size ofthe stent may need to be adjusted to compensate for the differing sizesof the vessel to be treated, bearing in mind the sizing guidelinesprovided above.

Having fully described a preferred embodiment of the invention, thoseskilled in the art will immediately appreciate, given the teachingsherein, that numerous alternatives and equivalents exist which do notdepart from the present invention. It is therefore to be understood thatthe present invention is not to be limited by the foregoing description,but only by the appended claims.

I claim:
 1. A method of manufacturing an endovascular support devicecomprisingforming a toroid from a first material, plating the toroidwith a second material having higher lubricity than the first material,bending the toroid to form a plurality of upper and lower peaks,stripping off the second material from the toroid, and reducing thediameter of the bent toroid to a desired size.
 2. A method ofmanufacturing an endovascular support device comprising:forming atoroid; and bending the toroid to form a plurality of upper and lowerpeaks.
 3. The method of claim 2 further comprising the step of reducingthe diameter of the bent toroid to a desired size.
 4. The method ofclaim 3 wherein the step of reducing the diameter of the toroid isperformed by etching.
 5. The method of claim 2 further comprising thesteps of:forming a plurality of toroids; and bending the plurality oftoroids to form a plurality of bent toroids having a selectable numberof upper and lower peaks.
 6. The method of claim 5 including theadditional steps of arranging the plurality of bent toroids to form theendovascular support device and reducing the diameter of the pluralityof bent toroids to a desired size.
 7. The method of claim 6 wherein theplurality of bent toroids forming the endovascular support device arenot connected to one another.
 8. A method of manufacturing anendovascular support device comprising the steps of:forming a memberhaving a plurality of upper and lower axial turns connected bysubstantially straight segments, wherein no straight segment overlapsany other straight segment; and reducing the cross-section of the memberto a desired size.
 9. The method of claim 8 wherein at least one of thesteps is performed by etching.
 10. The method of claim 8 wherein both ofthe steps are performed by etching.
 11. The method of claim 8 furthercomprising the step of:forming a plurality of members each having aplurality of upper and lower axial turns connected by substantiallystraight segments wherein no straight segment overlaps any otherstraight segment.
 12. The method of claim 11 further comprising the stepof:reducing the cross-section of each of the plurality of members to adesired size.
 13. The method of claim 11 wherein the plurality ofmembers forming the endovascular support device are not connected to oneanother.